A number of grammarians, teachers often think that punctuation, capitalization, spelling and grammar rules are absolute. The reality is that grammar hardly is black and white. It evolves over time, and depending on your current location in the world – the United States or the British Commonwealth; Canada or England – different rules generally are considered the norm of what constitutes proper English. Indeed, even within a country, various editors and teachers will espouse conflicting rules.

One such rule is that of the serial comma (aka the series comma, Oxford comma, or Harvard comma). For example, The MLA Style Manual, The Chicago Manual of Style, Strunk and White’s Elements of Style, and the U.S. Government Printing Office Style Manual all give one rule while the Associated Press Style Manual gives a contradictory rule…and the AP rule generally matches what most British style guides say, though even in Merry Ol’ England not all grammarians agree.

The serial comma rule issue centers on whether a comma is needed in a list. For example, in the sentence California, Oregon and Washington border the Pacific Ocean, should a comma appear after the second to last item on the list (Oregon)? The MLA Style Manual, The Chicago Manual of Style, Strunk and White’s Elements of Style, and the U.S. Government Printing Office Style Manual say “yes.” The Associated Press Style Manual and most British style guides say “no.”

Worse, these rules shift slightly when the listed items are phrases. Most stylebooks – including the Associated Press – say a comma is needed after the second to last item in a series of phrases, such as in the sentence: Common weapons used in science fiction stories include ray guys based on laser technology, disrupters that utilize concentrated sound waves, and plasma blasts of highly concentrated ionized gas.

When editing, I generally follow the Associated Press Style of Manual rules on the serial comma. Why? Because readers are less likely to think of it as an error as they primarily read media reports either in print or on the Internet that follow this style. In addition, many readers pick up books British Commonwealth authors who don’t use the Oxford comma in a series of single words.

All is relative, however. As a writer, you should follow a stylebook and stick to it. If your publisher follows The Chicago Manual of Style or your professor follow The MLA Style Manual, then that’s what you should go with. Whatever you do, be consistent with the style within the book.